Genesis and Evolution of Surface Species during Pt Atomic Layer Deposition on Oxide Supports Characterized by in Situ XAFS Analysis and Water−Gas Shift Reaction

Abstract

Platinum atomic layer deposition (ALD) using MeCpPtMe 3 was employed to prepare high loadings of uniformsized, 1-2 nm Pt nanoparticles on high surface area Al 2 O 3 , TiO 2 , and SrTiO 3 supports. X-ray absorption fine structure was utilized to monitor the changes in the Pt species during each step of the synthesis. The temperature, precursor exposure time, treatment gas, and number of ALD cycles were found to affect the Pt particle size and density. Lower-temperature MeCpPtMe 3 adsorption yielded smaller particles due to reduced thermal decomposition. A 300°C air treatment of the adsorbed MeCpPtMe 3 leads to PtO. In subsequent ALD cycles, the MeCpPtMe 3 reduces the PtO to metallic Pt in the ratio of one precursor molecule per PtO. A 200°C H 2 treatment of the adsorbed MeCpPtMe 3 leads to the formation of 1-2 nm, metallic Pt nanoparticles. During subsequent ALD cycles, MeCpPtMe 3 adsorbs on the support, which, upon reduction, yields additional Pt nanoparticles with a minimal increase in size of the previously formed nanoparticles. The catalysts produced by ALD had identical water-gas shift reaction rates and reaction kinetics to those of Pt catalysts prepared by standard solution methods. ALD synthesis of catalytic nanoparticles is an attractive method for preparing novel model and practical catalysts.

In situ synchrotron based x-ray techniques as monitoring tools for atomic layer deposition

“…[70][71][72] There are also reports of XAS as an in vacuo technique, where the sample can be transferred from the ALD chamber to an UHV system to allow for XAS. [36][37][38][39] To the best of our knowledge, the use of XAS as an in situ technique has been performed once on powderous supports in absorption mode 40 and once studying ALD growth on a planar support in fluorescence mode. 41 B. X-ray photoelectron spectroscopy XPS is a technique that allows the study of composition and chemical state of the elements in a material.…”

Mobile setup for synchrotron based in situ characterization during thermal and plasma-enhanced atomic layer deposition

“…In recent years, several groups have explored extending this concept of using light to study ALD growth towards the x-ray part of the electromagnetic spectrum. 8,[10][11][12][13][14][15][16][17][18][19][20][21][22][23] Indeed, when an ALD reactor is equipped with x-ray transparent windows (e.g., beryllium, graphite, or kapton), then the film can be (intermittently) exposed to x-rays during growth, and a wide range of x-ray based thin film characterization techniques can be used for in situ characterization, as recently reviewed by Devloo-Casier et al 17 Since ALD is typically used for nanocoatings with a thickness of 0.1 to several tens of nanometers, while xrays typically penetrate several micrometers deep into most materials, it is challenging to obtain a sufficient signal to noise ratio for x-ray based characterization techniques, in particular when targeting acquisition rates of 1-60 s in order not to interfere too much with the standard exposure cycle of the ALD process. Therefore, while lab-based x-ray sources are used routinely for ex situ analysis of, e.g., the crystallinity of ALD grown films, the in situ studies typically require the high photon flux that can only be offered by synchrotron based sources.…”

“…In situ XAS during ALD allows probing the local atomic environment and provides information such as the level of oxidation, coordination numbers, and bond lengths. 12,16,19 GISAXS is a scattering technique used to study the morphology of nanoscale objects at surfaces, interfaces, or in thin films. 30 In ALD research, in situ GISAXS has been applied to investigate conformal deposition in porous thin films 18 and on a layer of semiconducting quantum dots.…”

Scalable Production of Nanostructured Particles using Atomic Layer Deposition

“…The importance of Pt as a catalytic material has driven efforts for deposition on strontium titanate, titania, zirconia and alumina high-surface-area supports in the temperature window of 150-300°C (Christensen et al, 2009;Enterkin et al, 2011;Lobo et al, 2012;Setthapun et al, 2010;Xie et al, 2012). Moreover, the technique has also been used for the doping of Co-based Fischer-Tropsch catalysts with small amounts of Pt (0.1 wt.%) that acts as a promoter (Cronauer et al, 2011).…”